Hardening-off question

[michael4spoons]

Eventually I will be taking my seedlings from under the lights and setting them outside to harden-off. Question: after each day's round of hardening, should I bring them back inside and put them back under the lights, or instead should I bring them inside but NOT put them back under the lights?

[nctomatoman]

That is exactly where I am - what I did yesterday is put my seedling flats out in the sun for an hour - (it was calm and about 60 deg) - they then went back under the lights. Today I put them out for about 2 hours in the sun (same temp/still calm) - then back under lights. We may have a warm streak coming - eventually I will have them outside all day (I have very densely planted flats - at least 1000 tomato, pepper or eggplant seedlings, about 2 weeks post seeding - not yet at true leaf stage), probably within a week. Even if the cotyledon leaves get sunburned a bit, the plants will be fine - just be sure that they don't dry out.

[duajones]

I had a sungold that grew quicker than my other seedlings and before I knew it, it had grown into the bulbs, resulting in some burn on the leaves. once i noticed it and raised the light a bit, it grew on fine. I have since hardened it off and it is in the ground. The burns on the upper leaves are still visible but it looks fine otherwise. Should i be concerned or just let it grow?

[nctomatoman]

No worries. One year we had cold (35 degree), wind driven rain for 48 hours. Many of my seedlings looked half dead or more - leaves badly wind burned.....once things warmed up and they took off, they were fine.

Tomato seedlings are quite tough little buggers!

[melody]

I do what Craig does....I do the 'seedling flat dance' every spring. I have a south facing concrete area that is completely sheltered, so flats go out there on nice days for an hour or so.Then they are back under the lights. On nasty or cold days, they stay under the lights all day. It's amazing how sturdy and dark green they get from this short time outside. They also get a taste of actual breezes which strengthens the stems and makes them much easier to handle when i pot them up.

[carolyn137]

When I was growing hundreds and hundreds of plants I did not do the seedling tray dance.

My feeling is that you don't put them out until they are very close to being set out as transplants, so I'd put them outside only about a week before plant out time ( they had been grown cool in a farmer friend's greenhouse).

It seems to me that anything one might accomplish in terms of hardening off could be reversed by continually babying them taking them back inside. Such as toughening up the leaf epidermis, for instance.

Of course predicted frost or hard rains are sufficient reason for either covering them or moving them.

So I guess there's more than one way to look at this hardening off process and what it accomplishes and why so many folks do it, as do all of my commercial farmer friends, so it can't be all bad.

[michael4spoons]

Thanks, guys. Also sent this same question to tomatobob.com and Bob Price wrote back with the following answer:
"When we harden off plants, we usually keep them outside in a shaded area during the day and bring them inside a covered area (a garage is great) and let them rest in the dark. It is important that they do not get direct sunlight for several days as it can damage the leaves. A gentle breeze is also helpful as it helps to strengthen the stems."
For what it's worth, last year I put them back under the lights after each round of hardening (one hour; two hours; etc. for a week). Most did fine, but some went yellow. The yellowness could have been due to a fertilizer problem. This year will harden them a bit at a time but do as Bob suggests and bring them into the garage but not put them back under artificial lighting. Will see what happens and report on it here.